This invention relates generally to processes for the fabrication of thin film heads. More particularly, it relates to a process for planarizing a patterned metal structure for a magnetic thin film head.
In the continuing quest for increased storage density in magnetic media storage devices, magnetic thin film heads, such as magnetoresistive (MR) read/write heads or giant magnetoresistive (GMR) read/write heads, have been developed. As opposed to earlier types of magnetic heads, the fabrication of which involves significant piecework and manual handling of individual tiny components, thin film magnetic heads take advantage of semiconductor fabrication processes to form a large number of heads simultaneously on a common substrate or wafer.
In the prior art, sputtered amorphous aluminum oxide was used as a xe2x80x9cbackfillxe2x80x9d material before planarizing thin film head structures. These structures are often several microns thick, requiring hours of time on expensive vacuum sputtering equipment prior to planarization.
Spin-on processes have been used in the fabrication of thin film magnetic heads to planarize and smooth-out pits on the substrate. The use of silicon dioxide, applied as a wet xe2x80x9cspin on glassxe2x80x9d (SOG), is employed similarly in the semiconductor industry. Spin-on glasses are conventionally heated to temperatures exceeding 300xc2x0 C. to fully cure and harden the film.
U.S. Pat. No. 5,500,243, issued Mar. 19, 1996 to Danny D. L. Yang discloses a process for forming dielectric thin film coating on a substrate surface, which is suitable for use in magnetic thin film heads. The process of this Prior Art includes the application of a spin-on-glass (SOG) on a substrate, the spinning of the substrate, the preheating of the substrate and thin film to remove the solvents in the spin-on-glass material, and the heating in a reducing or in an inert atmosphere of the film to provide a conversion to a SiO2 film. The preheating step requires a temperature in range from 250xc2x0 C. and 330xc2x0 C., and the heating step requires temperature in range from 900xc2x0 C. and 1100xc2x0 C. This process only applies for coating a substrate before making magnetic thin film heads. This high temperature processing currently with SOG prevents it from being used later in the process since thin film head structures such as magnetoresistive (MR) and giant magnetoresistive (GMR) sensors are readily damaged by such high temperature.
The process of curing an insulating layer of a thin film head by an electron beam is well known in the prior art. An article titled xe2x80x9cElectron Beam Processing of Allied Signal Accuglass 211 SOGxe2x80x9d published in Jun. 16, 1994 by Allied Signal Electron Vision Group teaches an electron beam process, a non-thermal method, for processing spin-on-glass materials. The electron beam process does not require, but may be used in conjunction with, active heating of the substrate and material to achieve the desired cure. However, such processes have not been used in fabrication of MR and GMR heads.
There is a need, therefore, for an improved fabricating process for magnetic thin film heads that is efficient and not operated at high temperatures to overcome the above difficulties.
Accordingly, it is a primary object of the present invention to provide a process for planarizing patterned metal structures for magnetic thin film heads wherein:
1) the curing step is performed at temperature below 200xc2x0 C., so the damaging of the magnetic thin film head is prevented
2) the cycle time is short
3) costs are reduced
These and other objects and advantages will be apparent upon reading the following description and accompanying drawings.
These objects and advantages are attained by a process for planarizing patterned metal structures for a magnetic thin film head.
According to a preferred embodiment of the present invention, an encapsulation/planarizing material is applied on the surface of a substrate and an unplanarized magnetic pole or other structure(s) of a magnetic thin film head. The encapsulation/planarizing material typically includes silicon, oxide, aluminum oxide, titanium oxide or zirconium oxide, or inorganic or inorganic/organic polymers, which crosslink upon exposure to the energetic particles. Alternatively, the encapsulation/planarizing material may include high temperature croslinking organic polymers.
The substrate with applied encapsulation/planarizing material is spun in a photoresist spinner with a speed between about 1000 RPM and about 4000 RPM, for a time within the range of approximately 20 seconds to 180 seconds, at room temperature. After the spin-on step, the encapsulation/planarizing material is fully densified and cured using energetic particles such as electrons or photons. The curing step takes place at the substrate temperature less than 200xc2x0 C., for a time within the range of approximately 1 minute to 20 minutes. The cured encapsulation/planarizing layer is denser than the pre-cured material, resulting in a thinner layer than the initially applied encapsulation/planarizing layer. Finally, the entire structure is polished down to a level that exposes the magnetic poles or other structures in the thin film head.